The invention relates generally to the field of photography, and in particular to cameras. More specifically, the invention relates to a camera in which lens displacement or other control is accomplished using a shaped memory alloy driver.
Prior art U.S. Pat. No. 5,279,123 issued Jan. 18, 1994 mentions that shaped memory alloy (abbreviated to SMA) devices are well known in the art to undergo a martensitic (diffusionless) transition dependent upon the temperature applied to the SMA device. The SMA device when heated above its transition temperature undergoes a shape change to a memorized shape and when cooled below its transition temperature reverses the shape change from the memorized shape to an original shape. This change in shape can be used to provide mechanical work.
Often, as disclosed in prior art U.S. Pat. No. 5,459,544 issued Oct. 17, 1995, the SMA device is a fine metallic wire. When electrical current is applied to lead wires connected to opposite ends of the SMA wire, the SMA wire is heated to due to electrical resistance and it shrinks or contacts, i.e. recovers, to a memorized shape. When the electrical current is cut, the SMA wire cools to extend, i.e. deform, to an original shape. One application of the SMA wire to do mechanical work in U.S. Pat. No. 5,459,544 is a lens displacing mechanism for an objective lens, including an actuator pivotable in opposite directions to displace the objective lens in respective directions and an SMA wire which when heated contracts to its memorized shape to pivot the actuator forward to displace the objective lens forward and when cooled extends to its original shape to allow a return spring to pivot the actuator rearward to displace the objective lens rearward. The objective lens is displaced between two extreme positions, a close or near focus position and a far or infinity focus position, to change the actual distance between the lens and the film plane in a camera in order to adjust the image sharpness. Other applications of the SMA wire to do mechanical work in U.S. Pat. No. 5,459,544 include aperture adjustment, lens zooming movement, self-timer control, film winding, and shutter control.
Generally speaking, a control mechanism for use in a camera comprising an actuator movable to adjust an adjustable component in the camera, and a shaped memory alloy (abbreviated to SMA) wire which when heated contracts to a memorized shape to move the actuator to adjust the adjustable component, is characterized in that:
the SMA wire has opposite ends that are fixed in place and an intermediate movable portion between the opposite ends that directly contacts the actuator to move the actuator when the SMA wire is heated to contract. Preferably, the intermediate movable portion of the SMA wire has a longitudinal mid-point and directly contacts the actuator only substantially at the longitudinal mid point.
More specifically, a lens displacing mechanism for an objective lens comprising an actuator movable to displace the objective lens, and a shaped memory alloy (abbreviated to SMA) wire which when heated contracts to a memorized shape to move the actuator to displace the objective lens, is characterized in that:
the SMA wire has opposite ends that are fixed in place and an intermediate movable portion between the opposite ends that directly contacts the actuator to move the actuator when the SMA wire is heated to contract.